Graphite outgassing



July 22, 1947- J. E. WHITE l GRAPHITE AOU'J'GSSING Filed March 1,' 1945van.

INVENTOR J'. E VH/7'5" BY MAM l l u ATTORNEY heated in use.

-release of further gas from the anode.

Patented July V22, 1947 UNITED A STAT Corporation, ion of PennsylvaniaWestinghouse Electric burg'h, Pa., av corporat assigner toVlr EastPitts# Application Marchi, 1945, serial No'. sossrffv 4 claims. (ci.siczii- This invention relates to graphite outg'assin and has particularapplication to the electronic art and outgassing of such graphite'partsas an'- cdes, baies and the like, which are used Within anevacuated electronic device.

It is well appreciated in the electronic art that graphite parts have atendency to'release gas therefrom into an evacuated. container in whichsituated particularly when vsaid part becomes Presence of gas in anelectronic device will not only change its characteristics but in mostinstances renders the device inoperative for its intended purposes. Forinstance, an ignitron utilizes aV graphite anode, and in use may besubjected to intense heat atsome spot from an arc back. If the heat atthat spot liberates gas from the anode, the gaswill result in greaterionization in the ignitron, which in turn encourages further arc backs'with the probability of Thus the Vice iS 0u tbefpumpszbeing`evacuated.VSince the ignitron `musty of necessityV contain parts having ignitronbecomes progressively Worse and soon is useless for its intendedpurpose.l

Broadly considered, therefore,`the invention has for an object the moreperfect outgassing of graphite parts.

Likewise, from its most general aspect, the invention proposes theoutgassing of graphite parts at temperatrues exceeding any encounteredin use.

A further object of the invention is to protect the graphite part afterit is outgassed and' until incorporated in the electronic device so itmay` be then nally and adequately outgassed by normal procedure withother parts of the device.

Still further objects of the invention will Aappear to those skilledinthe art to which it appertains as the description progresses, bothI bydirect recitation thereof and by implication from the context.

In the accompanying drawing:

Figure 1 illustrates an ignitron having an anode of the charactertreated in accordance with the present invention; and

Figure 2 is a sectional view of anv apparatus forl carrying out theoutgassing of graphite parts in accordance With the invention.

By way of example, an ignitron is shown in l Figure 1 having a graphiteanode I0 suspended in a sealed envelope Ilv on the bottom header l2 ofAwhich is a mercury pool cathode I3 into which a starter electrode orignitor I4 is dipped. During manufacture of the ignitron, the same issub-v jected to as high a temperature as the character of its parts andjoints will permit, for purposes of freeing gas from internal parts andWhile the devite part,- Vand :in v the presv 4lower mel-tingftempe'ratures than 'thoseof the anode or. its envelopether.efisa'practicallix'nitatin on heat .which'can befsafel-'nl applied totlieanode after it -is mounted"A in "tl'iel ignitron'. Unfortu.- nately,thelimitation-i's tooiowtopermit'heat ing the'anode .to sufficientlyhigh temperature to :Attempts'havlesbe'enhere 1 the-anode",be1`or`eiritroducf ing it into thel ignitronpbut-ithasbeeri'fund thatA whenexposed toairmfmak ing transfer to the ignitrcn-,pabsorbs gasses frofmfthe air, wh'ich again socontannnatethe anode jj;

that normal outgassirigirifthe' 'gniton envelope thoroughly outgas -it.tofore Iliade to 'ontgaathe outg'a'ssed anode does not suiilce. 4According to the prese I0 as representativefof su the envelope. Ane1ectric"furnace` "Seis-shown inFi'gure 2 forfthe purpose,'jsaid'frnacel having I Y eral walls of the shell are heat shields t9serving to confine the greater part o f the developed heat to the-oven.The part, such as anode lfllto be outgassed is placedin the oven.Leadein co'nne'c'- tions 20'pass current to the heating element or ovenand by it a temperature Within the range of 180D" .C. to 2000 C. isfdeveloped inl the oven n Y and effective upon partfl.

Shell lli has apipe connection 2l to its interior from the exterior, andduringthe heating periodabove related, thisl pipe connection isjoined,fas.

through a valve'22y to a vacuumpump or system by which the oven isevacuated. The partfican be considered degassed when the pressure goesdown to .'75 micron at 1800 C. and when-fthe pumps can be shut off forone hour at i800 C. without the pressure rising above '3 microns.

When the degassing has thus been accomplished,: the temperature intheovenV is reduced to 200 C. or less, to be Within a temperature rangewherein an appropriate gas to be used, such-as hydrogen, or one ofthenoble gases such as helium, argon, neon. and so forth,`is practicallyinsoluble in solids. For brevity, the selected gas will be referred toas the protective gas. At that temperature condition of the oven,thevalve 22 (which forthe purpose is preferably a, threec h partgds treatedpri-or I',

-to being appliedinintended'place-j offuse withinvv instance.

way valve) is turned toadmit the said protective gas to the oven and llthe same to atmospheric pressure. The protective gas at this temperatureand pressure enters the surface pores oi the part I outgassed. Theprotective gas does not seem to penetrate to any considerable depth, and

yet by surface absorption or impregnation thereofin the anode, itconstitutes a protection against extraneous gases being absorbed whenthe anode is next exposed to air. This surface penetration of theprotective -gas is readily removedrby subsequent normal outgassingprocedure applied to the ignitron after transfer of the anode to itsappointed lplace therein. As indicated above, hydrogen and the noblegases are not dissolved in graphite to any objectionable extent, andthose gases are therefore readily removed at moderate temperatures. asmay have dissolved in the graphite, on being released during the highertemperature periods during exhaust, has a beneficial effect in removingtraces of injurious oxides which may have been left in the tubeinadvertently.

Consequently, after the hydrogen or other protectiveras has beenintroduced into the oven as above cited, the protective gas supply isshut offA and the furnace shell opened. The graphite part or anode I0 isthen promptly'transferred to its appointed place, as in the ignitronenvelope, and that envelope, with its contents, then subjected to theusual outgassing procedure. In this stage of operation, temperaturesfrom` about 800 C. and not exceeding 1200 C. are usually employed whilethe device is on the pump for evacuating said device or ignition in thepresent The protective surface infiltration of hydrogen or otherprotective gas present in the graphite part due to the pre-mounting andoutgassing procedure outlined above, is readily drawn from the anode atthis lower temperature; approximating 800 C. to 1200 C., and thus theanode is to all intents and purposes devoid of releasable gas. As aresult, arc-back spots in use on the anode,Y whichr are at a. lowertemperature 'than the primary outgassing temperature of 1800o C. to20,00" C.,have no gas-releasing effect, and the ignitron remains in goodevacuated condition free of evolved gas from the are back.

While the foregoing description has utilized graphite as an exemplarymaterial being out-V gassed and has referred to the part as an anode andas used in an ignitron as the device in which used, the invention is tobe understood as also applicable to other materials, parts and devices.

Such small amount of hydrogen I claim:

1. An outgassing method for a part to be used in an evacuated envelope,comprising outgassing the part at a temperature approximating 1800 C.,applying a surface impregnation of a protective gas to the outgassedpart, enclosing said part in an envelope, and outgassing said part insaid envelope at a less temperature than before.

2. An outgassing method for a part to be used in an evacuated envelope,comprising outgassing the part at a temperature in the approximate rangeof 1800` C. to 2000 C., reducing the temperature to approximately atenth of the said outgassing temperature, yapplying a protective gas toYthe vpart at its reduced temperature, enclosing said part in an envelopeand outgassing said part in said envelope at a less temperature than thefirst used outgassing temperature,

3. An outgassing method for a part to be used in an evacuated envelope,comprising outgassing the part before introduction into said envelope ata temperature in the approximate range of 1800 C. to 2000 C., reducingthe temperature to approximately 200 C., applying vhydrogen as aprotective surface impregnation to said part at its reduced temperature,transferring Vsaid part to and mounting it in an envelope for use,

' and again outgassing said part and in its final position in saidenvelope and at a temperature less than the said range of 1800 C. to2000"v C. and more than the approximate said temperature of' 200, C. atwhich the hydrogen was applied.

4. Anoutgassingmethod for a part 4to'be used in an evacuated envelope,comprising heating the part in vacuum toa temperature less than l itsmelting `point and'sirnultaneously outgassing the samebeforeintroduction into said envelope, cooling said part while still invacuum, and after cooling of said part admitting a protecting gasthereto, transferring said part to said envelope, and again heating, butat' a. lower temperature than the first said heating, and simultaneouslyoutgassing said part in the envelope.

JOHN E. WHITE.

REFERENCES CITED UNITED STATES PATENTS Name Date Spanner Dec. 26, 1939Number

